1. Field of the Invention
The present invention relates to a gas-insulated switchgear apparatus, more particularly relates to a gas-insulated switchgear apparatus including a cylindrical part that is mounted about a center conductor in a manner to surround it.
2. Description of the Related Art
Gas-insulated switchgears are used in the field of electrical power generation and transformation in electrical power systems. Gas-insulated switchgears are constituted by a pressure vessel that is filled with arc-extinguishing gas, and in which a switchgear, a bus bar, and a current transformer or a potential transformer are housed.
Conventionally, efforts have been made to downsize gas-insulated switchgears. One method of downsizing is to set the design value of an electric field at the vicinity of portions to be gas-insulated at a high level so as to shorten the insulation distance and thereby make the device size smaller. However, setting a high design value of the electric field at the vicinity of the portions to be insulated would cause any foreign matter (extraneous matter) in the device, which is otherwise harmless, to turn into a factor that might reduce the insulation reliability.
Unexamined Japanese Patent Application Publication No. 2004-56927 discloses a gas-insulated switchgear that has a capability of rendering a foreign matter harmless. The content of this publication is incorporated herein by reference.
The gas-insulated switchgear disclosed in this publication includes a metal adaptor that mounts a current transformer in the pressure vessel and that has an opening therein. A metallic foreign matter (metallic object) between the current transformer and the center conductor falls downward through the opening formed in the metal adaptor or from an end portion of the current transformer on the opposite side into a low electric field region and thereby is rendered harmless. This construction requires the metallic foreign matter to travel in the axial direction of the current transformer toward either end portion thereof before falling into the low electric field region, taking a long time to get rendered harmless. There is possibility that the metallic foreign matter existing between the current transformer and the center conductor reduces dielectric strength of the gas-insulated switchgear, resulting in low insulation reliability of the gas-insulated switchgear.